The Spells Wild Slash gets the maindeck nod over Fiery Impulse because you want to be able to cast it at any time to get value out of your Prowess creatures, most importantly Monastery Mentor
Adding Threats On the flip side, you can also use your sideboard to find a new threat that your opponent will struggle with
Right now, Pioneer is dominated by Rakdos Demons and Gruul Aggro, and, discounting Izzet Phoenix, there really aren't many graveyard-focused decks at the top of the meta
The card wasn't corrected in the regular Revised print run, so despite its notoriety, it's not particularly valuable
Erikas Invitation may be expensive in this incarnation, but theres a second full art variant also available thats around half the price
For sure, although it will be far from the best draw in the deck